WHAT'S THE DIFFERENCE BETWEEN A PRIMARY KEY AND A UNIQUE KEY?

Chintoo Semi

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  1. Chintoo Semi

    Post:79

    Points:395
    What's the difference between a primary key and a unique key?

    Both primary key and unique key enforces uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.

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